As power conditioners of photovoltaic power generation systems and power devices used for motor revolution control, more products have been designed in modules, e.g., a package of multiple power devices, in order to reduce a footprint, improve performance with a shorter distance between semiconductor elements, and reduce a design load for users.
Packaged products are called power modules. Such power modules contain IGBTs (insulated gate bipolar transistors) for switching and power semiconductor elements such as MOSFETs (Metal-Oxide-Semiconductor Field Effect Transistors). Modules particularly called IPMs (Intelligent Power Modules) contain multiple driver elements for driving power semiconductor elements and further contain multiple passive elements if necessary with the function of driving and protecting power semiconductors. Such modules have expanded a new market.
The structure of such a power module is typically manufactured as follows: a power semiconductor element bonded on a ceramic substrate is mounted on a resin-molded frame called an insert case, the terminals of the case and the surface of the power semiconductor element are connected with metallic wires such as Al wires, and then the terminals and the power semiconductor element are potted with silicone gel so as to be collectively molded.
However, a heat sink attached to the back side of the insert case may be warped depending upon the module size or structure, making it difficult to obtain flatness on the back side. In this case, the power module attached to the heat sink via heat sink grease may vary in the thickness of the heat sink grease depending upon the location. A portion having a large thickness considerably decreases in heat dissipation efficiency and thus may cause thermal destruction in the power module.
A solution to this problem is disclosed in Patent Literature 1.
FIGS. 10(A) and 10(B) are plan views of a semiconductor device 100 described in Patent Literature 1. FIG. 10(B) is a cross-sectional view of FIG. 10(A).
The semiconductor device 100 includes a case 101 and at least two packages 102. The case 101 is composed of a resin-molded frame including external terminals 103 and output terminals 104. Tapped holes 105 for connection to a heat sink (not shown) are provided on the four corners of the case 101. The package 102 includes, for example, a metal block 106 made of Cu. An insulating substrate 114 made of materials such as ceramic is fixed on the back side of the metal block 106. On the metal block 106, a power semiconductor element 108 is fixed via a metallic lead frame 107. The power semiconductor element 108 is, for example, a MOSFET or an IGBT. The surface electrodes of the power semiconductor element 108 are connected to inner leads 110 via bonding wires 109 made of materials such as Al with a diameter of about 300 μm.
The metal block 106 and the power semiconductor element 108 are molded with mold resin 111, e.g., epoxy resin so as to partially expose the lead frame 107.
From the mold resin 111, power terminals 112 and control terminals 113 are drawn and exposed. The power terminals 112 are connected to the external terminals 103 and the output terminals 104 of the case 101. The control terminals 113 are drawn from a different side from the power terminals 112 drawn from the mold resin 111.
A method for manufacturing the semiconductor device will be briefly described below.
First, the lead frame 107 is fixed on the metal block 106 and then the power semiconductor element 108 is mounted thereon. After that, the metal block 106, the lead frame 107, and the power semiconductor element 108 are resin-molded using a transfer molding apparatus. Specifically, the lead frame 107 with the fixed metal block 106 and so on is disposed in molds, and then epoxy resin is poured into the molds to form the mold resin 111.
In this case, the back side of the metal block 106 is exposed from the mold. After the mold resin 111 is formed, the metal block 106 is removed from the molds, and then the insulating substrate 114 is joined to the back side of the metal block 106 with solder or the like.
Finally, an unnecessary part of the lead frame 107 is removed, and then the lead frame 107 is processed into a desired shape to form the power terminals 112 and the control terminals 113. Thus, the assembly of the package 102 is completed.
Subsequently, as shown in FIGS. 10(A) and 10(B), the packages 102 are placed into the case 101, and then the external terminals 103 and the output terminals 104 are connected to the power terminals 112. For example, solder or the like is used for the connection. The power terminals 112 are connected to the external terminals 103 and the output terminals 104 so as to fix the packages 102 in the case 101.